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Meta·Data Scientist·Technical Phone Screen·Senior

Senior
May 2026

Summary

Meta DS interview with a meaty SQL question on content moderation prevalence metrics. One question, but it packed in a lot: window logic, ex-ante vs ex-post definitions, aggregation, and a creator-level breakdown. The kind of problem where you can get the easy parts right and still miss the subtle stuff.

Questions Asked (1)

Q1

Given tables for content views, content moderation decisions, and content metadata, write SQL to compute daily view prevalence of violating content by country over a 7-day window. You need two variants: ex-ante prevalence (a view counts as violating only if a violation decision existed at or before the view timestamp) and ex-post prevalence (based on the final decision regardless of detection timing). Then find the top 3 creators by ex-post violating view share and break down their violating views by surface.

Product Analytics & MetricsData Modeling
Author's notes

The ex-ante vs ex-post distinction is where most of the complexity lives.

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AI HintsAI Generated

Suggested Approach

Clarify the schema and definitions first, then build a modular SQL solution: compute ex-ante and ex-post violation flags per view, aggregate daily prevalence by country, and finally rank creators by ex-post violating view share and break down by surface. Use CTEs to keep logic readable and testable.

Pro tip: Explicitly state your assumptions about the data (e.g., one moderation decision per content, view timestamps in UTC) and validate edge cases like multiple decisions or missing metadata before writing the final query.

1. Clarify schema and definitions

Confirm table structures, join keys, and what constitutes a 'violating' decision (e.g., decision = 'violation'). Define ex-ante (decision timestamp <= view timestamp) and ex-post (any final violation decision) precisely.

2. Compute per-view violation flags

Join views with moderation decisions and metadata. Create two flags: ex_ante_violation (1 if a violation decision existed at or before view time) and ex_post_violation (1 if the content was ever decided as violating).

3. Aggregate daily prevalence by country

Group by date, country, and surface (if needed) to compute total views and violating views. Calculate prevalence as violating views / total views for both ex-ante and ex-post over the 7-day window.

4. Rank creators by ex-post violating view share

Aggregate views by creator, compute ex-post violating view share, and rank creators to find the top 3. Ensure you handle ties or minimum view thresholds if appropriate.

5. Break down top creators' violating views by surface

For the top 3 creators, group their ex-post violating views by surface and compute counts or shares. Present the breakdown clearly.

Key Points to Mention

  • Use of CTEs for modularity and readability
  • Handling of time zones and timestamp comparisons
  • Definition of ex-ante vs. ex-post and how they differ in SQL logic
  • Aggregation functions and window functions for ranking
  • Potential data quality issues: multiple decisions per content, missing metadata, or duplicate views
  • Performance considerations: indexing on join keys and date filters

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.